Incrementally assemble a tar file, with streaming

[johnpyp]

Describe the feature

I'd like to be able to incrementally assemble the tar file with files that may be too big to fit into memory (all the files together may be too big to fit into memory upfront, or even individual files).

Similar functionality to what https://github.com/mafintosh/tar-stream I believe

Additional information

• Would you be willing to help implement this feature?